Again what make a Stack Exchange site different then a forum or a Q&A site like Yahoo Answers is the reputation system. It does a good job of identifying good questions and answers. More importantly giving those who do give good questions and answers more responsibility for running the site. At the highest reputation there is little difference between the original moderators and the user.
Plus there enough a game aspect that it is fun to try to ask good question and give good answers
MorrisonMP asks some good questions
First off Jeff Atwood (one of the founders/coders of Stack Overflow and a very good programmer talks about it here.
1. What makes a question a "good" question?The short answer any question you have about running or playing a tabletop RPG. A slightly longer answer are the example questions on the site. However the key element is the reputation system filtering the "good" questions from the "bad" questions. You don't know what is a good question until you post and read through the comments, answers, up votes, and down votes. From my experience on Stack Overflow it is self policing after the community gets going.
2. What makes an answer a "good" answer? (and the answer to this seems obvious, but what I meant is, good as defined by the reputation system.)Again the reputation system defines what are good answers.
3. If the reputation system is based on voting, how will this in any way keep the same vocal minority that is the majority on forums from doing the same here?If you notice they require a lot of committed people in order to put this up on line. The idea that with such a large number it will be hard for a minority to hijack the site. Also those who already have high reputations on other Stack Exchange sites count more in the commitment process (I have a 4000+ rep on Stack Overflow). In theory this means that those of us with high reps learned to "play nice" under this system.
From following Stack Exchange they try to get a bunch of little things going together in synergy rather relying on one big idea. Note they have a badge system in addition to raw reputation.
4. Once reputation begins to be set, it becomes increasingly difficult to alter, so what stops people from bumping themselves to the top of the pile?There is a maximum per day. It also flags repeated votes from the same group IPs to counteract friends voting for each other all the time.
Ultimately, how does this method actually improve on the forum mechanic -- since it still relies on the same controls (peer) that ultimately set the communication rules of forum sites.
The focus of Forums is on organizing discussions. Stack Exchange was built on getting good answers and good questions first then organizing discussions. The shift in focus makes a difference. Programming forums have a problem with programming language wars which rival editions wars in RPGs. If you look on Stack Overflow you will see it relatively free of that. Proponents of different languages inhabit the same site peacefully which is a miracle in of itself.
The initial months will be crucial, if the community treats the Roleplaying Stack Exchange site like Stack Overflow users then it will a good resource. If it is highjacked then traffic will fall and the Stack Exchange folks will close it.